Precision 28918A 8-Channel CVLD/IEPE Conditioner

Transcription

1 On the New Frontiers of Precision Precision 28918A 8-Channel CVLD/IEPE Conditioner The 28918A 8-Channel CVLD/IEPE Conditioner is a member of the Precision 28 family of signal conditioners. The 28918A provides conditioning for CVLD accelerometers and IEPE (Integrated Electronic Piezoelectric) accelerometers. The 28918A is a dual mode card operating in either CVLD mode or IEPE Mode. In CVLD Mode, small AC current signals are detected even in the presence of large noise voltage common with cabling in high magnetic field environments. The constant voltage excitation is programmable to 1 or 15 V. A buffered system test bus signal provides compatibility with CVLD sensors equipped with sensor cal input. In IEPE mode, the 28918A is compatible with either floating or grounded sensors with programmable IEPE current up to 12 ma. The 28918A provides an overall amplifier gain up to 124 and up to 3 khz filtered or 19 khz wideband bandwidths A Applications Vibration Measurements in high magnetic noise environments Platform noise Structure-borne noise Acoustic receivers Load, torque, dynamic force, dynamic pressure, shock, vibration and acoustic measurements Machine health monitoring Structural response tests Precision 28918A Features Eight channels per card 128 channels per 2816-M3 or 2816-M5 mainframe, 64 channels per 288-M3/M5 mainframe, 32 channels per 284-M3/M5 mainframe 16 channels pre 282-M5 mainframe IEPE, CVLD or voltage inputs Isolated IEPE mode to break cabling ground loops Up to 3 khz filtered bandwidth or 19 khz wide-band bandwidth Compatible with single-ended Constant Voltage Line Drive (CVLD) sensors with 2-wire (coaxial) connections Programmable IEPE current to, 4, 8 12 ma Programmable CVLD excitation 1 or 15 V Programmable amplifier: x½ to x124 with.5 x steps 4-pole low-pass filters with filter bypass (wide-band) 2 phase matching between any channels, 1 Hz to Fc.2 typical phase match 1 Hz to 3 khz (unfiltered) Overload detection Sensor CAL signal for CAL equipped CVLD sensors Precision 28918A for the 28 Analog Signal Conditioner Overview 28 Analog Signal Conditioning System The new standard for the world s most discriminating test labs. The Precision 28 signal conditioning system provides all the flexibility you need to manage your test measurements. The Precision 28 makes it easy to manage a test, with hundreds of channels and a mix of transducers. Choose charge, IEPE w/teds, voltage (filter amplifier), strain, thermocouple, RTD, potentiometer, current, frequency, or other transducers. The built-in test hardware and software (optional) provide quick Go/No-Go tests, which can be run before each test, and rigorous Factory Acceptance Tests to assure you that the 28 meets your most stringent requirements for critical applications. It won t be long before these tests earn a permanent place in your maintenance routine. And since they are traceable to NIST, they eliminate the need for off-site calibration. In every phase of your tests record keeping, installation, design, setup, operation, maintenance, and upgrading the Precision 28 offers ways to help you save time and money over the life of the system. 28 System Features Graphical user interface (GUI) and Ethernet network interface for system control Intelligent gain and system scaling algorithms Test input and output monitor busses Go/No-Go test with diagnostics to be used before tests Rigorous Factory Acceptance Test for maintenance Field-swappable AC power supplies Built-in temperature and power supply monitoring with alarms Page 1

2 Precision 28918A Description Precision 28918A Description CVLD Mode While cable shielding is very effective at reducing electrostatic noise coupling, it does little to prevent noise coupling due to severe magnetic interference. Since magnetically induced noise is modeled as a noise voltage induced into the sensor cable, it is very disruptive to high sensitivity voltage measurement circuits such as the IEPE accelerometer. Special CVLD accelerometers were developed for magnetic environments that present the vibration signal as a variable current rather than variable voltage. If the attached signal conditioner is sensitive to AC current flow and insensitive to voltage signals, then we can exploit the unique characteristic of the CVLD accelerometer to acquire low-level vibration signals even in the presence of large magnetic interference. The CVLD Mode of the 28918A is compatible with CVLD accelerometers and detects small AC current signals even in the presence of large noise voltage common in high magnetic field environments. Constant voltage excitation is programmable to 1 or 15 V to accommodate various CVLD sensor models. Some CVLD sensors have a third wire test signal input that is used to inject a test signal into the CVLD sensor for full end-to-end system checkout. The 28918A is compatible with these sensors and provides a buffered version of the system test bus signal. This signal can be placed individually on each channel or simultaneously on all system channels. The CVLD sensor has internal electronics, which convert the piezoelectric vibration signal to an output loop drive current. A sudden change of bias current to these internal circuits is a good predictor of sensor malfunction, and could indicate that the sensor should be taken out of service. In CVLD mode, the 28918A continually monitors excitation voltage and bias current into the CVLD sensor. These two parameters are combined together and presented to the user as a single value representing health of the sensor as described by EXC+Bias = EXC+I(bias) * 4. An example of a typical EXC+Bias reading for a CVLD sensor is shown below. Excitation setting = 15V Bias Current = 1mA EXC+Bias = 15+1mA * 4= 19V In addition to a visual readout of the EXC+Bias value, user programmed upper and lower fault limits can trigger a gage fault indicator which is clearly visible on the GUI and readable by host software communicating via LCS. IEPE Mode In IEPE mode, the 28918A accommodates long cable runs with programmable IEPE current up to 12 ma. Isolated inputs break cabling ground loops associated with triaxial accelerometer or grounded accelerometer cases. Visibility of the DC bias level is a crucial aspect of IEPE sensors as the sensors bias voltage is a useful indicator of sensor, cable and connector health. The 28918A card IEPE input stage continually monitors the DC bias voltage present on the channel input. This voltage level is displayed for each channel and is compared to user programmable upper and lower threshold limits to alert the user to a sudden shift of the bias level. A system bias level report can be requested at any time, creating a file for pre-test gage health documentation. Amplifier and Filter Programmable pre- and post-filter amplifiers provide an overall gain of 124. Gain is distributed both before and after the filter to provide protection from large out-of-band energy or transients that could cause clipping before the filter, distorting the data. The Gain Wizard in the GUI allows the user to set a gain reserve and then apportions the gain between the input and output. This provides input gain for best noise performance yet conforms to the limitations of the user s worst case estimate of out-band or transient signals. Overload detectors alert the user to over-voltage conditions. The 28918A contains a 4-pole low-pass filter with cutoffs settings of 3 Hz, 1 khz, 3 khz, 1 khz, and 3 khz and programmable flat or pulse mode. The flat mode provides pass-band characteristics nearly identical to a Butterworth filter while providing a much sharper roll-off. This mode is a good choice for applications such as spectral analysis. The pulse mode has time domain response similar to the Bessel filter yet provides superior amplitude response characteristics. The pulse mode is ideal for time domain applications including transient (shock) measurements and time domain waveform analysis. External Pre-Amp Power: For applications utilizing low nose acoustic sensors with remote pre-amplifiers, the 28918A has built in regulator circuits that provide power to remote pre-amplifiers. Pre-amp output signal can be connected to 28918A high impedance inputs with 28918A in Filter/Amp mode. Up to 2 ma of regulated and fused pre-amp power is available for each channel on the 28918A input connector. +15 V pre-amp power is provided on the standard 28918A model, however other voltages between +26 and 15 V can be specified on as a custom model. Page 2 Precision Filters, Inc.

3 28918A Details and Specifications 28918A Conditioner Cards The detailed description and specifications for the 28918A are organized in the following sections: Programmable Features Input Characteristics Filter/Amplifier Mode input Characteristics Amplifier Characteristics Filter Type Characteristics Test Modes Output Characteristics General Characteristics Connectors Accessories Ordering Information 28918A Programmable Features CVLD Mode Sensor power: Programmable to, 1 or 15 V Sensor calibration (on or off) Sensor power monitor with programmable fault limits (upper and lower limits) CVLD substitution current (On/Off) IEPE Mode IEPE current (, 4, 8, 12 ma) Bias monitor with programmable fault limits (upper limit and lower limit) Input mode (IEPE conditioner or differential input filter/amp) AC current dither Isolated (sensor grounded) or grounded (sensor isolated) IEPE/CVLD Common Features Gain (½X to 124X) Cutoff frequency: (3 Hz, 1 khz, 3 khz, 1 khz, and 3 khz) Wide band 19 khz (filter bypassed) Test modes: run (operate), input short, cal voltage substitution (Test Bus) Input Characteristics IEPE Inputs (IEPE Mode) Type: Programmable grounded (sensor floating) or isolated (sensor grounded) Connector: High, low and shield per channel on high-density 26-pin connector IEPE Current:, 4, 8, 12 ma or disconnect Current Accuracy: ±1% Maximum Input: 22 V (DC bias + AC signal) IEPE Current Noise: 13 pa/ Hz Frequency Response (Filter Bypass): 1.17 Hz to 19 khz Amplifier Noise: 15 nv/ Hz RTI at 1 khz and pre-gain >x16 CVLD Mode Type: Single-ended. Input low connected to system ground. Connector: High, low, cal and shield per channel on high-density 26-pin connector Sensor Excitation: Programmable, 1 or 15 V Sensor Excitation Accuracy: 5% Maximum Input: 22 ma (bias + signal current) Input Sensitivity: 4 mv/ma Frequency Response (Filter Bypass): 1.17 Hz to 19 khz Current Conversion Accuracy:.2% (Vout/Iin), typical Sensor Calibration: Test signal for CVLD sensors equipped with sensor cal input Sensor Cal On: Buffered test bus signal applied to sensor cal connection Sensor Cal Off: Sensor cal connector biased to sensor power Accuracy:.2% (1 Hz to 1 khz) Noise: 5 pa/ 1kHz Line Voltage Rejection: 8 db DC to 1 khz 6 db to 1 khz CVLD Substitution: CVLD sensor disconnected, internal CKTS inject CVLD simulation test current to CVLD input stage Level:.5 ma per 1 V test bus signal Accuracy:.2% (1 Hz to 1 khz) Page 3

4 28918A Details and Specifications Filter/Amplifier Mode Input Characteristics Note: Specs at 25 C unless otherwise noted. Common Mode V: ±1 V operating CMRR: 8 db DC to 1 khz Input Protection: ±3 V Input Impedance: (.1 μf & 5 MΩ)//1 pf per side AC Coupling Frequency: 1.17 Hz ( 3 db) Max Level: ±1 Vpk for f 1 khz; ±1 Vpk (1 khz/f) for f>1 khz Noise: 15 nv/ Hz RTI at 1 khz and pre-gain >x8 typical Pre-Amp Power Current: +2 ma max per channel Pre-Amp Power Accuracy: ±2% Pre-Amp Power Spectral Noise: 2.5 µv/rthz 28918A Amplifier Characteristics Pre-filter Gain: x1 to x 64 in binary steps with overload detection (1.5 Vpk threshold) Post-filter Gain: x½ to 16 in.5% of setting Overall Gain: x½ to x124 vernier adjustment of.5% of setting Distortion:.1% re Fullscale Frequency Response (Bypass Mode): 3.1 db Bandwidth, 1 Hz to 19 khz, typical 5% Bandwidth: 3.5 Hz to 13 khz 1% Bandwidth: 8 Hz to 1 khz Bypass (Unfiltered) High Frequency Rolloff: 18 db/octave 28918A Channel Block Diagram IEPE Module SE/DIFF Overload Post-Filter Gain High Low +EXC CVLD Module Amp Pre-Filter Gain LP Programmable 4-Pole Filtered Unfiltered Prog. Buffered Amp Output 4 + Auto Calibrate Gain & Offset Monitor Bus CVLD Substitution Sensor CAL Pre-Amp Power Power Return Shield V(DC) Test Input Input Short 28918A Channel Simplified Block Diagram Page 4 Precision Filters, Inc.

5 28918A Filter Characteristics You want your analog data to come clean before digital conversion. Flat/Pulse Low-Pass Filters Our P 4-pole flat/pulse low-pass filters provide the user with the versatility to address applications in either the time or frequency domain and are available on many 28 card models. Flat Mode Low-Pass Filters Precision flat mode characteristics are specified to have outstanding passband flatness equivalent to the Butterworth yet deliver very sharp roll-off characteristics. The is a good choice as an anti-aliasing filter and for applications such as spectral analysis. The has zero passband ripple and roll-off superior to the Butterworth. Pulse Mode Low-Pass Filters For the time domain, program the lowpass filter to pulse mode. These filters have excellent transient response and phase linearity making them ideal filters for time domain applications including transient (shock) measurements and time domain waveform analysis all with roll-off characteristics superior to their Bessel filter counterparts. and LP4P Amplitude Response vs Butterworth Passband Response Gain (db) LP4P Normalized Frequency (f/fc) Gain (db) & 4-Pole Butterworth Normalized Frequency (f/fc) vs Butterworth Amplitude Response Gain (db) Pole Butterworth Normalized Frequency (f/fc) LP4P vs Bessel Passband Response.5 Gain (db) Pole Bessel LP4P Normalized Frequency (f/fc) LP4P vs Bessel Step Response 1.4 Response/Final Value LP4P.2 4-Pole Bessel (for Comparison) Time x Fc (Sec x Hz) and LP4P Step Response 1.4 Response/Final Value LP4P LP4P.8 1-9% Rise (Sec).39/Fc.34/Fc 5% Delay (Sec).45/Fc.28/Fc.6 % Overshoot 11.1%.5%.4 1% Error (Sec).96/Fc.48/Fc 5% Error (Sec) 1.9/Fc.54/Fc.2 1% Error (Sec) 1.65/Fc.66/Fc.5% Error (Sec) 2.14/Fc.7/Fc.1% Error (Sec) 2.72/Fc.77/Fc Time x Fc (Sec x Hz) Page 5

6 28918A Filter Characteristics 28918A Filter Type Characteristics Filter Type: P: 4-pole, 4-zero low-pass filter. Programmable for maximally flat pass-band () or linear phase with optimized pulse response (LP4P). Cutoff Frequencies: FX2: 3 Hz, 1 khz, 3 khz, 1 khz, 3 khz Amplitude Accuracy: ±.1 db max, DC to.8 Fc ±.2 db max,.8 Fc to Fc Amplitude Match: ±.1 db max, DC to.8 Fc ±.2 db max,.8 Fc to Fc Phase Match: ±1 max, DC to.8 Fc ±2 max,.8 Fc to Fc Filter Bypass: Bypasses filter but not amplifier stages. Bypass Bandwidth: 19 khz, typical Custom Filters: Other filter characteristics and cutoff frequencies are available. Please consult with factory for more information. Specification Maximally Flat Low-Pass Filter LP4P Constant Time Delay Low-Pass Filter Cutoff Frequency Amplitude 3.1 db 3.1 db DC Gain. db. db Pass-Band Ripple. db. db Stop-Band Frequency ( 8 db) Fc Fc Cutoff Frequency Phase 18. deg 11.5 deg Phase Distortion (DC to Fc) < 31.8 deg < 3.7 deg Zero Frequency Group Delay.4117/Fc.292/Fc Percent Overshoot 11.1%.5% 1% Settling Time 1.65/Fc.66/Fc.1% Settling Time 2.72/Fc.77/Fc.1 db Frequency.6348 Fc.1816 Fc 1 db Frequency.8487 Fc.5742 Fc 2 db Frequency.937 Fc.8129 Fc 3.1 db Frequency 1. Fc 1. Fc 2 db Frequency Fc Fc 4 db Frequency Fc Fc 6 db Frequency Fc 9.98 Fc 8 db Frequency Fc Fc Page 6 Precision Filters, Inc.

7 28918A Details and Specifications 28918A Test Modes Sensor Cal: (CVLD Mode only) Test Bus signal is applied to test output line. A buffered (per channel) version of the cal signal is output through the input connector via a separate wire to be used with transducers with a calibration input. Amplifier Short: A switch at the amplifier input is utilized to ground the input stage for measurement of noise and DC offset. CVLD Substitution (CVLD Mode only): CVLD sensor is disconnected, internal circuits inject simulation current into CVLD input stage Test Bus: Test input allows for injection of a test signal. An external test signal or the 28-?-TEST Test Subsystem may be connected at the rear panel. Refer to the 28-?-TEST Test Subsystem specification for more information. AC Current: (IEPE Mode only) An AC dither current is summed with the IEPE current to create an AC voltage signal based on the transducer s output impedance. AC current is derived from test bus voltage according to: AC Current = V (Test Bus)/ A Output Characteristics Type: Two independently buffered single ended outputs Z: 1 Ω shunted by 1 pf Max Output: ±1 Vpk, ±5 ma pk Noise: 6 µvrms RTI + 6 µvrms RTO, typical 3 Hz to 1 khz Crosstalk: 8 db, DC to 25 khz between channels with the same configuration and programmed settings Output Monitor (Standard) A switch located at the output of each channel allows for multiplexed connection to the mainframe output monitor bus. The output monitor bus is available at a connector located at the rear of the mainframe. The monitor function is used by the Test Subsystem or is available to the user for viewing channel output. Input Preamp Prog. Filter Post Amp Output CH Transducer Interface + LP Programmable 4-Pole FP CH M5-RP CH Test Bus Bypass Monitor Bus CH 127 Test Bus Transducer Interface + Bypass LP Programmable 4-Pole Monitor Bus FP CH 127 M5-RP CH F-BIF1-FT Backplane Interface Card Linear Power Supply 2816 Mainframe Test Bus 28-?-TEST Test Subsystem Monitor Bus GPIB or Ethernet PC Controller RS-232 Ethernet Page 7

8 28918A Accessories and Ordering General Characteristics 28918A Card Size: 6.63 x 17.5 x.75 inches Card Weight: 1.4 lb. net Temperature: C to 4 C (operating); 2 C to 7 C (storage) Connectors The input connectors are integral to the 28918A card. Cutouts on the 28 frames allow the 28918A input to pass through the backplane and mate directly with the input cables. Three 26-pin high-density D I/O connectors are utilized, two for the 8 inputs on the rear panel and one for the 8 outputs on the front panel of the card. Connectors have high quality machined gold plated pins/sockets. Three wires per output are provided to accommodate twisted/shielded cables. Accessories Mating Connectors Precision Filters mating connectors accommodate up to 22-AWG wire and are supplied with high-quality metal backshells and gold plated screw machined contacts for high reliability connections and long service life. CONN-IN-26D High-density 26-pin D-shell mating input connector with machined crimp pins and metal backshell with strain relief. CONN-IN-26D-SC High-density 26-pin D-shell mating input connector with machined solder cup pins and metal backshell with strain relief. CONN-OUT-26D High-density 26-pin D-shell mating output connector with machined crimp pins and metal backshell with strain relief. CONN-OUT-26D-SC High-density 26-pin D-shell mating output connector with machined solder cup pins and metal backshell with strain relief. Test Adapter and Test Cables: CB-2898/28918A-TEST-ADAPTER: Input test adapter module for Factory Acceptance Test (FAT). CB-REF-C: Reference cable for FAT match tests on M3 chassis. CB-HD26P-REF-C: Reference cable for FAT match tests on M5 chassis. Precision PF-1U-FA Multi- Channel Programmable Filter/Amplifier System Exceptional desktop performance. Ideal for conditioning low-level voltage inputs in front of high-resolution digital data acquisition systems. Fully programmable 8-channel and 16-channel configurations are available, both offering a choice of either 4 or 8-pole low-pass filters with programmable gain. High Density Programmable Switch Systems Computer controlled analog signal switching replaces tedious manual patch panels. Precision x64 Switch Matrix System 28918A Card Model Number The 28918A card model number describes the configuration of the eight channels on the card. The model number identifies the filter type of the low-pass and cutoff frequencies A-<Cutoff Frequencies>-P <VP? VN?> FX2: 3 Hz, 1 khz, 3 khz, 1 khz, 3 khz Pre-Amp Voltage Level: 15 V to +26 V Pre-Amp Voltage Polarity: N = Negative, P = Positive VP15 Standard Precision 464kC Switch Matrix System Precision switch systems are reliable solid-state switch matrix systems, providing computer-controlled connection between input and output signals. Configure the 464kC with up to 256 inputs and 256 outputs, all in a single mainframe, or choose the compact 4164 system with 64 inputs and 64 outputs. Save time and reduce errors on test system setup. Download switch configurations from the host computer over the network. Built-in self-test with fault diagnostics. P8525 Rev - ISO 91 CERTIFIED QUALITY Precision Filters, Inc. 24 Cherry Street Ithaca, New York 1485 Telephone: pfinfo@pfinc.com Web Site: